Windows form a large portion of the exterior surface area of many buildings. When light enters the building through the windows, the interior is heated by the light energy. In summer, such interior heating of the building increases the air conditioning demand, and thence the consumption of electrical power.
A number of techniques have been proposed to control the heating of the interior of the building by the light entering the windows. One commonly used approach is exterior window shades and awnings that block all wavelengths of the sunlight incident at higher angles, but allow a person in the building to look out through the window at normal and near-normal incidence angles (measured in the vertical plane) to the window. These shades and awnings are highly effective in controlling interior heat loading, but reduce the visibility through the windows.
Exterior window shades and awnings can be used on residences and other smaller buildings, but they cannot be used effectively in high-rise buildings. Other heat-control techniques have been devised for such buildings. Because the human eye sees only in the visible spectrum, “low E” window coatings have been designed to block the infrared portion of sunlight, allowing the visible portion of the sunlight to enter the window largely unimpeded. Indium-tin-oxide (ITO) coatings are an example of such infrared-blocking coatings. Tints have also been employed on the window glass to reduce the transmission of light energy.
These techniques have been only partially effective for high-rise and other buildings for which exterior window shades and awnings cannot be used. There is a need for a better approach to controlling the introduction of heat by transmitted sunlight into the interiors of buildings. The present invention fulfills this need, and further provides related advantages.